Bacterial Exofactors Modulate Biofilm Growth and Resistivity to Antimicrobial Drugs

Some bacteria have the ability to co-exist, proliferate and survive in a multicellular community, biofilm. Each participating bacteria can form its colonies and encases itself by a self-produced insoluble extracellular matrix substance (EPS). Microcolonies within biofilm are held together by interactions and bonding of the substances present in the EPS with their separation from the water channels. Similar to insoluble EPS, bacterial microcolonies release soluble exofactors that have direct impacts on the survivability, growth and antibacterial resistivity of other microcolonies made of single- or multi-species bacteria in the same biofilm. How the exofactors of microcolonies of one-type bacteria impact on microcolonies of other-type bacteria is still unclear. We studied about the role of exofactors released from Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa, which are common biofilm-forming pathogenic bacteria. Exofactors facilitate to transform the microenvironment where bacteria can acquire alternative lifestyle with a long survival period and resistivity to certain antimicrobial drugs.

Biofilm three-dimensional architecture influences in situ pH distribution pattern on the human enamel surface

To investigate how the biofilm three-dimensional(3D) architecture influences in situ pH distribution patterns on the enamel surface. Biofilms were formed on human tooth enamel in the presence of 1% sucrose or 0.5% glucose plus 0.5% fructose. At specific time points, biofilms were exposed to a neutral pH buffer to mimic the buffering of saliva and subsequently pulsed with 1% glucose to induce re-acidification. Simultaneous 3D pH mapping and architecture of intact biofilms was performed using two-photon confocal microscopy. The enamel surface and mineral content characteristics were examined successively via optical profilometry and microradiography analyses. Sucrose-mediated biofilm formation created spatial heterogeneities manifested by complex networks of bacterial clusters(microcolonies). Acidic regions(pH<5.5) were found only in the interior of microcolonies,which impedes rapid neutralization(taking more than 120 min for neutralization). Glucose exposure rapidly re-created the acidic niches, indicating formation of diffusion barriers associated with microcolonies structure. Enamel demineralization(white spots),rougher surface, deeper lesion and more mineral loss appeared to be associated with the localization of these bacterial clusters at the biofilm-enamel interface. Similar 3D architecture was observed in plaque-biofilms formed in vivo in the presence of sucrose. The formation of complex 3D architectures creates spatially heterogeneous acidic microenvironments in close proximity of enamel surface, which might correlate with the localized pattern of the onset of carious lesions(white spot like) on teeth.

Global Proteomics of the Extremophile Black Fungus <i>Cryomyces antarcticus</i>Using 2D-Electrophoresis

The microcolonial black fungus Cryomyces antarcticus is an extremophile organism growing on and in rock in the Antarctic desert. Ecological plasticity and stress tolerance make it a perfect model organism for astrobiology. 2D-gel electrophoresis and MALDI-TOF/TOF mass spectrometry were performed to explore the protein repertoire, which allows the fungus to survive in the harsh environment. Only a limited number of proteins could be identified by using sequence homologies in public databases. Due to the rather low identification rate by sequence homology, this study reveals that a major part of the proteome of C. antarcticus varies significantly from other fungal species.

Phylogeny and taxonomy of meristematic rock-inhabiting black fungi in the Dothideomycetes based on multi-locus phylogenies

The last decade has revealed an unexpected fungal diversity associated with natural rocks,often collected in environments influenced by harsh climatic conditions.Yet the phylogenetic affiliations and the taxonomy of many of these extreme fungi,mainly within Dothideomycetes,the largest class of Ascomycota,have only partially been described.In the present study we confirm that most rock inhabiting-fungi(RIF)are highly polyphyletic among Dothideomycetidae,mainly within the order Capnodiales,an order otherwise incorporating several families of major plant pathological importance.Novel taxa were identified within the two major and distinct clades of Teratosphaeriaceae,both comprising meristematic black fungi.Thirty one novel species and 13 new genera are proposed,based on ITS and partial nucLSU,RPB2 and BT2 sequences.

Extremotolerant rock inhabiting black fungi from Italian monumental sites

A wide sampling for isolating highly destructive and extremotolerant black fungi was performed from Italian monuments in selected historical sites which include the "Cortile della Pigna",Vatican Museum and the St Peter colonnade(Vatican City State),the monumental cemetery of Bonaria(Cagliari),and other monuments in the city of Cagliari.Thirty out of seventy-four strains isolated were identified basing on ITS Blastn comparison.Based on multilocus phylogeny and morphological data,one new genus and species Lithophila guttulata,five new species Knufia marmoricola,K.vaticanii,K.karalitana,K.mediterranea and Exophiala bonariae,order Chaetothyriales and one new genus and species,Saxophila tyrrhenica,and two new species Vermiconia calcicola and Devriesia sardiniae,order Capnodiales,were proposed.Ecological considerations are put forward.

Mountain tips as reservoirs for new rock-fungal entities: Saxomyces gen. nov. and four new species from the Alps

As part of a worldwide sampling nine black fungi were isolated from rocks collected in four distinct sites of the Alps at high altitudes.Based on a nucSSU,nucLSU and mtSSU multi-locus phylogeny,seven of them were found to cluster into a distinct and wellsupported clade in a basal position within the Class Dothideomycetes.As in other rock fungi these new groups of isolates were characterized by a meristematic growth and a scarcely differentiated morphology with highly melanized and thick-walled toruloid hyphae.Nonetheless,few peculiar characters were also observed as convoluted hyphal tips and the production of spherical propagules.The new genus and species Saxomyces alpinus and S.penninicus,are here described based on morphological and molecular data,in a yet to be defined order of the Dothideomycetes.The remaining two black fungi clustered in Cryomyces,a genus previously exclusively found in rocks from the McMurdo Dry Valleys in Antarctica.These two isolates were genetically distant from other Antarctic Cryomyces species based on ITS sequences,and they showed a peculiar morphology;they are here described as the new species C.montanus and C.funiculosus.Implications of our results on the evolution,adaptation and dispersal of rock-inhabiting fungi under extreme conditions are discussed.